Asset Retirement Obligations (Tables)

6 Months Ended

Jun. 30, 2021

Asset Retirement Obligation Disclosure [Abstract]

Change in asset retirement obligations

The following schedule shows the change in our asset retirement obligations for the six months ended June 30, 2021 (dollars in thousands): 

	2021
Asset retirement obligations at January 1, 2021	$	705,083
Changes attributable to:
Accretion expense	18,828
Settlements	(2,853)
Estimated cash flow revisions	10,932
Asset retirement obligations at June 30, 2021	$	731,990